This invention generally relates to the extrusion of tubular articles. More particularly, this invention relates to an extrusion head for controlling the eccentricity or concentricity of an extruded tubular article. Specifically, this invention relates to such an extrusion head wherein a portion of the head itself is physically deflected to give the desired control of article concentricity.
In the extrusion of tubular articles, such as pipe, from molten material, such as thermoplastic, a continuing problem is control of the concentricity of the finished product. It is undesirable to have a final product which exhibits wall thickness variations when viewed in cross section. To this end, U.S. Pat. No. 3,923,439 purposes the use of movable slides within the extrusion head to compensate for concentricity variations in the output product. This system, while effective, requires a complex and expensive internal mechanism for the extrusion head. I have found that the concentricity of an output tubular article can be adequately controlled by physically deflecting part of the extrusion head with respect to a fixed extrusion mandrel over which the molten material is formed into the final tubular article.